The recently released Windows Azure Storage Client Library for .Net includes many new features, expanded platform support, extensibility points, and performance improvements. In developing this version of the library we made some distinct breaks with Storage Client 1.7 and prior in order to support common paradigms across .NET and Windows Runtime applications. Additionally, we have addressed distinct pieces of user feedback from the forums and users we’ve spoken with. We have made great effort to provide a stable platform for clients to develop their applications on and will continue to do so. This blog post serves as a reference point for these changes as well as a migration guide to assist clients in migrating existing applications to the 2.0 release. If you are new to developing applications using the Storage Client in .Net you may want to refer to the overview here to get acquainted with the basic concepts. This blog post will focus on changes and future posts will be introducing the concepts that the Storage Client supports.
Namespaces
The core namespaces of the library have been reworked to provide a more targeted Intellisense experience, as well as more closely align with the programming experience provided by other Windows Azure Services. The root namespace as well as the assembly name itself have been changed from Microsoft.WindowsAzure.StorageClient to Microsoft.WindowsAzure.Storage. Additionally, each service has been broken out into its own sub namespace. For example the blob implementation is located in Microsoft.WindowsAzure.Storage.Blob, and all protocol relevant constructs are in Microsoft.WindowsAzure.Storage.Blob.Protocol. Note: Windows Runtime component will not expose Microsoft.WindowsAzure.Storage.[Blob|Table|Queue].Protocol namespaces as they contain dependencies on .Net specific types and are therefore not projectable.
The following is a detailed listing of client accessible namespaces in the assembly.
- Microsoft.WindowsAzure.Storage– Common types such as CloudStorageAccount and StorageException. Most applications should include this namespace in their using statements.
- Microsoft.WindowsAzure.Storage.Auth – The StorageCredentials object that is used to encapsulate multiple forms of access (Account & Key, Shared Access Signature, and Anonymous).
- Microsoft.WindowsAzure.Storage.Auth.Protocol – Authentication handlers that support SharedKey and SharedKeyLite for manual signing of requests
- Microsoft.WindowsAzure.Storage.Blob – Blob convenience implementation, applications utilizing Windows Azure Blobs should include this namespace in their using statements
- Microsoft.WindowsAzure.Storage.Blob.Protocol – Blob Protocol layer
- Microsoft.WindowsAzure.Storage.Queue – Queue convenience implementation, applications utilizing Windows Azure Queues should include this namespace in their using statements
- Microsoft.WindowsAzure.Storage.Queue.Protocol – Queue Protocol layer
- Microsoft.WindowsAzure.Storage.Table – New lightweight Table Service implementation based on OdataLib. We will be posting an additional blog that dives into this new Table implementation in more greater detail.
- Microsoft.WindowsAzure.Storage.Table.DataServices –The legacyTable Service implementation based on System.Data.Services.Client. This includes TableServiceContext, CloudTableQuery, etc.
- Microsoft.WindowsAzure.Storage.Table.Protocol – Table Protocol layer implementation
- Microsoft.WindowsAzure.Storage.RetryPolicies - Default RetryPolicy implementations (NoRetry, LinearRetry, and ExponentialRetry) as well as the IRetryPolicy interface
- Microsoft.WindowsAzure.Storage.Shared.Protocol – Analytics objects and core HttpWebRequestFactory
What’s New
- Added support for the .NET Client Profile, allowing for easier installation of your application on machines where the full .NET Framework has not been installed.
- There is a new dependency on the three libraries released as OdataLib, which are available via nuget and codeplex.
- A reworked and simplified codebase that shares a large amount of code between platforms
- Over 450 new unit tests published to GitHub
- All APIs that execute a request against the storage service are marked with the DoesServiceRequest attribute
- Support for custom user headers
- OperationContext– Provides an optional source of diagnostic information about how a given operation is executing. Provides mechanism for E2E tracing by allowing clients to specify a client trace id per logical operation to be logged by the Windows Azure Storage Analytics service.
- True “synchronous” method support. SDK 1.7 implemented synchronous methods by simply wrapping a corresponding Asynchronous Programming Model (APM) method with a ManualResetEvent. In this release all work is done on the calling thread. This excludes stream implementations available via Cloud[Page|Block]Blob.OpenRead and OpenWrite and parallel uploads.
- Support for Asynchronous cancellation via ICancellableAsyncResult. Note this can be hooked up to .NET cancellation tokens via the Register() method as illustrated below:
…
ICancellableAsyncResult result = container.BeginExists(callback, state);
token.Register((o) => result.Cancel(), null /* state */);
…
- Timeouts – The Library now allows two separate timeouts to be specified. These timeouts can be specified directly on the service client (i.e. CloudBlobClient) or overridden via the RequestOptions. These timeouts are nullable and therefore can be disabled.
- The ServerTimeout is the timeout given to the server for each request executed in a given logical operation. An operation may make more than one requests in the case of a Retry, parallel upload etc., the ServerTimeout is sent for each of these requests. This is set to 90 seconds by default.
- The MaximumExecutionTime provides a true end to end timeout. This timeout is a client side timeout that spans all requests, including any potential retries, a given operation may execute. This is disabled by default.
- Full PageBlob support including lease, cross account copy, and read/write streams
- Cloud[Block|Page]Blob DownloadRange support
- Blobs support download resume, in the event of an error the subsequent request will be truncated to specify a range at the correct byte offset.
- The default MD5 behavior has been updated to utilize a FIPS compliant implementation. To use the default .NET MD5 please set CloudStorageAccount.UseV1MD5 = true;
Breaking Changes
General
- Dropped support for .NET Framework 3.5, Clients must use .Net 4.0 or above
- Cloud[Blob|Table|Queue]Client.ResponseReceived event has been removed, instead there are SendingRequest and ResponseReceived events on the OperationContext which can be passed into each logical operation
- All Classes are sealed by default to maintain consistency with Windows RT library
- ResultSegments are no longer generic. For example, in Storage Client 1.7 there is a ResultSegment<CloudTable>, while in 2.0 there is a TableResultSegment to maintain consistency with Windows RT library.
- RetryPolicies
- The Storage Client will no longer prefilter certain types of exceptions or HTTP status codes prior to evaluating the users RetryPolicy. The RetryPolicies contained in the library will by default not retry 400 class errors, but this can be overridden by implementing your own policy
- A retry policy is now a class that implements the IRetryPolicy interface. This is to simplify the syntax as well as provide commonality with the Windows RT library
- StorageCredentials
- CloudStorageAccount.SetConfigurationSettingPublisher has been removed. Instead the members of StorageCredentials are now mutable allowing users to accomplish similar scenarios in a more streamlined manner by simply mutating the StorageCredentials instanceassociated with a given client(s) via the provided UpdateKey methods.
- All credentials types have been simplified into a single StorageCredentials object that supports Anonymous requests, Shared Access Signature, and Account and Key authentication.
- Exceptions
- StorageClientException and StorageServerException are now simplified into a single Exception type: StorageException. All APIs will throw argument exceptions immediately; once a request is initiated all other exceptions will be wrapped.
- StorageException no longer directly contains ExtendedErrorInformation. This has been moved inside the RequestResult object which tracks the current state of a given request
- Pagination has been simplified. A segmented result will simply return up to the maximum number of results specified. If a continuation token is received it is left to the user to make any subsequent requests to complete a given page size.
Blobs
- All blobs must be accessed via CloudPageBlob or CloudBlockBlob, the CloudBlob base class has been removed. To get a reference to the concrete blob class when the client does not know the type please see the GetBlobReferenceFromServer on CloudBlobClient and CloudBlobContainer
- In an effort to be more transparent to the application layer the default parallelism is now set to 1 for blob clients. (This can be configured via CloudBlobClient.ParallelOperationThreadCount) In previous releases of the sdk, we observed many users scheduling multiple concurrent blob uploads to more fully exploit the parallelism of the system. However, when each of these operations was internally processing up to 8 simultaneous operations itself there were some adverse side effects on the system. By setting parallelism to 1 by default it is now up to the user to opt in to this concurrent behavior.
- CloudBlobClient.SingleBlobUploadThresholdInBytes can now be set as low as 1 MB.
- StreamWriteSizeInBytes has been moved to CloudBlockBlob and can now be set as low as 16KB. Please note that the maximum number of blocks a blob can contain is 50,000 meaning that with a block size of 16KB, the maximum blob size that can be stored is 800,000KB or ~ 781 MB.
- All upload and download methods are now stream based, the FromFile, ByteArray, Text overloads have been removed.
- The stream implementation available via CloudBlockBlob.OpenWrite will no longer encode MD5 into the block id. Instead the block id is now a sequential block counter appended to a fixed random integer in the format of [Random:8]-[Seq:6].
- For uploads if a given stream is not seekable it will be uploaded via the stream implementation which will result in multiple operations regardless of length. As such, when available it is considered best practice to pass in seekable streams.
- MD5 has been simplified, all methods will honor the three MD5 related flags exposed via BlobRequestOptions
- StoreBlobContentMD5 – Stores the Content MD5 on the Blob on the server (default to true for Block Blobs and false for Page Blobs)
- UseTransactionalMD5 – Will ensure each upload and download provides transactional security via the HTTP Content-MD5 header. Note: When enabled, all Download Range requests must be 4MB or less. (default is disabled, however any time a Content-MD5 is sent by the server the client will validate it unless DisableContentMD5Validation is set)
- DisableContentMD5Validation – Disables any Content-MD5 validation on downloads. This is needed to download any blobs that may have had their Content-MD5 set incorrectly
- Cloud[Page|Block]Blob no longer exposes BlobAttributes. Instead the BlobProperties, Metadata, Uri, etc. are exposed on the Cloud[Page|Block]Blob object itself
- The stream available via Cloud[Page|Block]Blob.OpenRead() does not support multiple Asynchronous reads prior to the first call completing. You must first call EndRead prior to a subsequent call to BeginRead.
- Protocol
- All blob Protocol constructs have been moved to the Microsoft.WindowsAzure.Storage.Blob.Protocol namespace. BlobRequest and BlobResponse have been renamed to BlobHttpWebRequestFactory and BlobHttpResponseParsers respectively.
- Signing Methods have been removed from BlobHttpWebRequestFactory, alternatively use the SharedKeyAuthenticationHandler in the Microsoft.WindowsAzure.Storage.Auth.Protocol namespace
Tables
- New Table Service Implementation - A new lightweight table implementation is provided in the Microsoft.WindowsAzure.Storage.Table namespace. Note: For backwards compatibility the Microsoft.WindowsAzure.Storage.Table.DataServices.TableServiceEntity was not renamed, however this entity type is not compatible with the Microsoft.WindowsAzure.Storage.Table.TableEntity as it does not implement ITableEntity interface.
- DataServices
- The legacy System.Data.Services.Client based implementation has been migrated to the Microsoft.WindowsAzure.Storage.Table.DataServices namespace.
- The CloudTableClient.Attach method has been removed. Alternatively, use a new TableServiceContext
- TableServiceContext will now protect concurrent requests against the same context. To execute concurrent requests please use a separate TableServiceContext per logical operation.
- TableServiceQueries will no longer rewrite the take count in the URI query string to take smaller amounts of entities based on the legacy pagination construct. Instead, the client side Lazy Enumerable will stop yielding results when the specified take count is reached. This could potentially result in retrieving a larger number of entities from the service for the last page of results. Developers who need a finer grained control over the pagination of their queries should leverage the segmented execution methods provided.
- Protocol
- All Table protocol constructs have been moved to the Microsoft.WindowsAzure.Storage.Table.Protocol namespace. TableRequest and TableResponse have been renamed to TableHttpWebRequestFactory and TableHttpResponseParsers respectively.
- Signing Methods have been removed from TableHttpWebRequestFactory, alternatively use the SharedKeyLiteAuthenticationHandler in the Microsoft.WindowsAzure.Storage.Auth.Protocol namespace
Queues
- Protocol
- All Queue protocol constructs have been moved to the Microsoft.WindowsAzure.Storage.Queue.Protocol namespace. QueueRequest and QueueResponse have been renamed to QueueHttpWebRequestFactory and QueueHttpResponseParsers respectively.
- Signing Methods have been removed from QueueHttpWebRequestFactory, alternatively use the SharedKeyAuthenticationHandler in the Microsoft.WindowsAzure.Storage.Auth.Protocol namespace
Migration Guide
In addition to the detailed steps above, below is a simple migration guide to help clients begin migrating existing applications.
Namespaces
A legacy application will need to update their “using” to include:
- Microsoft.WindowsAzure.Storage
- If using credentials types directly add a using statement to Microsoft.WindowsAzure.Storage.Auth
- If you are using a non-default RetryPolicy add a using statement to Microsoft.WindowsAzure.Storage.RetryPolicies
- For each Storage abstraction add the relevant using statement Microsoft.WindowsAzure.Storage.[Blob|Table|Queue]
Blobs
- Any code that access a blob via CloudBlob will have to be updated to use the concrete types CloudPageBlob and CloudBlockBlob. The listing methods will return the correct object type, alternatively you may discern this from via FetchAttributes(). To get a reference to the concrete blob class when the client does not know the type please see the GetBlobReferenceFromServer on CloudBlobClient and CloudBlobContainer objects
- Be sure to set the desired Parallelism via CloudBlobClient.ParallelOperationThreadCount
- Any code that may rely on the internal MD5 semantics detailed here, should update to set the correct MD5 flags via BlobRequestOptions
Tables
- If you are migrating an existing Table application you can choose to re-implement it via the new simplified Table Service implementation, otherwise add a using to the Microsoft.WindowsAzure.Storage.Table.DataServices namespace
DataServiceContext (the base implementation of the TableServiceContext) is not threadsafe, subsequently it has been considered best practice to avoid concurrent requests against a single context, though not explicitly prevented. The 2.0 release will now protect against simultaneous operations on a given context. Any code that may rely on concurrent requests on the same TableServiceContext should be updated to execute serially, or utilize multiple contexts.
Summary
This blog posts serves as a guide to the changes introduced by the 2.0 release of the Windows Azure Storage Client libraries.
We very much appreciate all the feedback we have gotten from customers and through the forums, please keep it coming. Feel free to leave comments below,
Joe Giardino
Serdar Ozler
Veena Udayabhanu
Justin Yu
Windows Azure Storage
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